title: Phosphorylation and degradation of S6K1 (p70S6K1) in response to persistent JNK1 Activation.
abstract: S6K (ribosomal S6 kinase p70, p70S6K) activation requires phosphorylation at two stages. The first phosphorylation is independent of insulin stimulation and mediated by an unknown kinase. The second phosphorylation is mediated by mTOR in insulin dependent manner. In this study, we identified JNK1 (c-Jun N-terminal kinase 1) as a kinase in the first phosphorylation. S6K protein was phosphorylated by JNK1 at S411 and S424 in the carboxyl terminal autoinhibitory domain. The phosphorylation was observed in kinase assay with purified S6K as a substrate, and in cells after JNK1 activation by TNF-α or MEKK1 expression. The phosphorylation was detected in JNK2 null cells, but not in JNK1 null cells after TNF-α treatment. When JNK1 activation was inhibited by MKK7 knockdown, the phosphorylation was blocked in cells. The phosphorylation led to S6K protein degradation in NF-κB deficient cells. The degradation was blocked by inhibition of proteasome activity with MG132. In wide type cells, the phosphorylation did not promote S6K degradation when IKK2 (IKKβ, IκB kinase beta) was activated. Instead, the phosphorylation allowed S6K activation by mTOR, which stabilizes S6K protein. In IKK2 null cells or cells treated by IKK2 inhibitor, the phosphorylation led to S6K degradation. These data suggest that S6K is phosphorylated by JNK1 and the phosphorylation makes S6K protein unstable in the absence of IKK2 activation. This study provides a mechanism for regulation of S6K protein stability.
authors.affiliation: Antioxidant and Gene Regulation Laboratory, Pennington Biomedical Research Center, Louisiana State University System, Baton Rouge, LA 70808, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.forename: Zhanguo
authors.initials: Z
authors.lastname: Gao
authors.forename: Jianping
authors.initials: J
authors.lastname: Ye
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism; D047468:Immunoprecipitation; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit / Q000502:physiology*; D010766:Phosphorylation; D059748:Proteolysis; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D052002:NF-kappa B p50 Subunit; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D025801:Ubiquitin; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; D051550:I-kappa B Kinase; C496562:Ikbkb protein, mouse; D048055:Mitogen-Activated Protein Kinase 8
keywords: Inflammation; Insulin resistance; Liver; Obesity; TNF-α